In October 2000 Australian Railroad Group were announced as the successful bidder for Westrail with operations commencing on 17 December 2000. Under the deal 95 locomotives, 2,500 wagons, freight terminals and customer contracts were purchased with the infrastructure remaining in government ownership, and leased to ARG for 49 years.[4][5]

Initially trains in Western Australia operated under the Australia Western Railroad name, with AWR logos being applied to locomotives in the orange, black and yellow of Genesee & Wyoming. With ARG's involvement with the Asia Pacific Transport Consortium building the Alice Springs to Darwin line, resulting in some locomotives operating construction trains on the line receiving Australia Northern Railroad logos, it was decided to rebrand all ANR, ASR and AWR operations under the Australian Railroad Group banner from August 2002.[3]

With the introduction of the ARG name and corporate colours, ARG began a gradual process of standardising the locomotive classification based on horsepower, with a progressive (and still incomplete) renumbering. As of February 2006 new letter classes will be used in conjunction with the new horsepower based numbering system (The Z on the end of some class letters refers to locomotives fitted with ZTR).